This invention relates to a variable capacity vane compressor, and more particularly to improvements in a bearing arrangement for a drive shaft and a capacity control element used in a variable capacity vane compressor.
A variable capacity vane compressor for use in automotive air conditioners has been proposed by Japanese Provisional Patent Publication (Kokai) No. 63-205493, which comprises, as shown in FIG. 1, a cylinder formed by a pair of side blocks 3, 4, and a cam ring 1 having opposite ends closed by the associated side blocks 3, 4, a rotor 2 rotatably received within the cylinder, and a drive shaft 7 on which the rotor 2 is rigidly fitted. The side blocks 3, 4 have respective through holes 40, 141 through which the drive shaft 7 extends. Radial bearings 8, 9 are force-fitted in the respective through holes 40, 141 for supporting the drive shaft 7. The rear side block 4 has an annular recess 23 formed in a rotor side end face 4a thereof. A capacity control element 124 in the form of an annulus is rotatably fitted in the annular recess 23 for controlling timing of start of compression of a refrigerant gas. The control element 124 is supported by a thrust bearing 143 fitted in an annular recess 142 formed in an inner peripheral surface of the through hole 141 of the rear side block 4. The thrust bearing 143, which is sandwiched between and end wall 142a of the annular recess 142 facing toward the rotor 2 and an opposed side face 124a of the control element 124, supports the control element 124 only in the axial direction.
The control element 124 is directly fitted on the drive shaft 7, with its central through hole 124b penetrated by the shaft 7.
As shown in FIG. 2, the opposed side face 124a of the control element 124 has a pair of pressure-receiving protuberances 26, 26 formed thereon. One side face of each pressure-receiving protuberance receives suction pressure Ps and an urging force exerted by a torsion coiled spring 38 having one end thereof engaged in a rear head 6, whereas the other side face of same receives control pressure Pc, whereby, responsive to a difference between the sum of the suction pressure Ps and the urging force of the torsion coiled spring 38 and the control pressure Pc, the control element 124 rotates between the maximum capacity position and the minimum capacity position to vary the capacity or delivery quantity of the compressor between the maximum value and the minimum value.
However, the control element 124 is also biased in the radial direction so that, as shown in FIG. 3, the central through hole 124b of the control element 124 is disposed excentrically to the drive shaft 7. That is, the inner peripheral surface of the central through hole 124b is constantly in line contact with the outer peripheral surface of the drive shaft 7 as shown in FIG. 3 such that the control element 24 is guided by the drive shaft 7 during rotation. Consequently, when the compressor 7 rotates at a high speed or the compressor is in a high load condition, there can occur galling between the control element 124 and the drive shaft 7, which prevents smooth rotation of the control element, resulting in degraded controllability of the compressor, and causes the drive shaft 7 and the control element 124 to be rapidly worn, resulting in degraded reliability.
In order to eliminate these inconveniences, a variable capacity vane compressor having an improved bearing for the capacity control element has been proposed by U.S. Ser. No. 07/680,414 assigned to the present assignee, which has already been allowed.
According to this proposed compressor, as shown in FIG. 4, the control element 123 is fitted on a central annular projection 146a of a rotor side race 146 of a thrust bearing 143. The other race 144 of the thrust bearing 143 is received in an annular recess 142 formed in the inner peripheral surface of the through hole 141, and an annular member 145 force-fitted in the annular recess 142 and urging the race 144 against an end wall 142a thereof facing toward the rotor 2. The rotor side race 146 with the control element 124 fitted thereon is fitted in the annular member 145. Part of the circumference of the rotor side race 146 is in slidable contact with an inner peripheral surface 145a of the annular member 145, while the rest of the circumference is spaced from the inner peripheral surface 145a by the maximum distance .delta. (e.g. 30 to 50 .mu.) as shown in FIG. 4. On the other hand, inner peripheral surfaces 146c, 146d of the respective central annular projection 146a and race 146 are spaced from the outer peripheral surface of the drive shaft 7 by a distance range S of e.g. 80.mu..+-.20.mu. along the whole circumference thereof.
Thus, according to this bearing arrangement, the control element 124 is guided during rotation thereof by the inner peripheral surface 145a of the annular member 145, so that the inner peripheral surface 146c of the annular projection 146a which is force-fitted in the hole 124b of the control element and the inner peripheral surface 146d of the race 146 are always kept out of contact with the outer peripheral surface of the drive shaft 7. This makes it possible to prevent occurrence of galling between the control element 124 and the drive shaft 7 even when the drive shaft 7 rotates at a high speed or when the compressor is in a high load condition, and also reduce wear of the component members.
However, the side blocks 3, 4 are formed of aluminum or an aluminum alloy, while the radial bearings 8, 9 are formed of a ferrous material. Therefore, the bearing arrangement of this compressor including the thrust bearing 143 and the radial bearing 9 has the following disadvantage: Since the aluminum alloy has a coefficient of thermal expansion larger than the ferrous material, a gap between the radial bearing 9 and the inner peripheral surface of the through hole 141 of the rear side block 4 increases when the rear side block 4 and the radial bearing 9 undergo expansion due to an increase in the temperature during operation of the compressor, which causes noise due to chattering between the radial bearing 9 and the rear side block 9.